Influence of Proteasome Inhibition on the Baker's Yeast Transcription Factor Yap1p Following its Activation by Organic Electrophiles

Abstract

Cells have evolved a variety of mechanisms to protect against adverse environmental conditions. In baker's yeast, the transcription factor Yap1p controls the activation of expression of detoxification genes that ultimately protect against cellular stress caused by oxidants and electrophiles. While Yap1p oxidation is reversible by the thioredoxin protein reductase system, the mechanism of Yap1p inactivation following its modification by electrophiles has not been elucidated. Here, I tested the hypothesis that electrophile-modified Yap1p is targeted for degradation by the proteasome. To this end, I conducted assays using a Yap1p-regulated reporter gene in the presence of the proteasome inhibitor MG132 and the electrophilic compound diethyl acetylenedicarboxylate (DAD). The data from these experiments indicate that proteasome inhibition does not significantly influence Yap1p activation by electrophiles. In a separate line of investigation, I studied Yap1p degradation by monitoring its levels in the presence of MG132 and the electrophiles, DAD and diethyl maleate (DEM). I found that MG132 increases Yap1p levels in the presence of the two electrophiles. Collectively, the results from these experiments indicate that proteasome inhibition plays a role in increasing Yap1p levels in the presence of electrophiles. Further investigation would help in identifying the proteasome as an inactivation pathway for electrophile-modified Yap1p.